Furnace hood



Nov; 10, 1970 I J. M. HEENEY 3,539,692

I FURNACE HOOD Filed June 24. 1969 2 Sheets-Sheet 1 INVENTOR. JOHN M. HEENEY ATTORNEY J. M. HEENEY Nov. 10, 1970 FURNACE HOOD 2 Sheets-Sheet 2 Fild June 24, 1969 I NVEN'TOR. JOHN M. HEENEY ATTORNEY US. Cl. 13-9 United States Patent Oiifice ABSTRACT OF THE DISCLOSURE A hood for an electrical arc furnace having openings in the roof for passage of heating electrodes therethrough and comprising a circular enclosure with electrode openings therein for mounting on the furnace roof about the electrodes and having a collector duct concentric about the electrodes, and bafile means in the interior of the duct about a portion only of the collector duct and being of a size and shape so as to provide a substantially equal pressure drop across the entire area of collector duct when suction is applied.

BACKGROUND OF THE INVENTION In use, electric arc furnaces emit large volumes of fumes and dust which must be controlled, which fumes and dust escape from the furnaces primarily from the openings in the roof of the furnace through which the heating electrodes project into the interior of the furnace. Fume and dust control are obtained presently by the use of a variety of types of suction hoods, which types, while generally operable, are not completely satisfactory. Canopy hoods, for example, are ones not physically attached to the furnace in any way, but are spaced above it to collect the fumes. Because of their remote location from the furnace, large air volumes are required when using such hoods to entrap the fumes and dust. Moreover, air currents within the plant itself interfere with proper collection of the fumes and dust. Also such hoods sweep the hot fumes up the electrodes, heating the electrodes and thereby resulting in a lower current density and more rapid melting time.

Full roof hoods, while requiring lower air volumes than the canopy type hood, are undesirable since they become distorted due to furnace heat, unless water cooled, and add undesired weight to the furnace roof support beams, and also undesirably heat the electrodes.

The roof tap and snorkle type hoods, while requiring the lowest amounts of air volumes, must be extremely carefully regulated to provide the proper furnace internal shell pressure.

SUMMARY OF THE INVENTION A furnace hood has now been found which directs dilution air countercurrent to the direction of the emitted fumes, resulting in more efficient capture of the fumes and also in cooling of the electrodes, thereby permitting higher electrode current density and increased electrode life and which provide a substantially uniform pressure drop at all points of fume collection from the furnace, which in turn has the advantage that the air, or other gas, requirement is maintained at a minimum.

Briefly stated, the present invention comprises a hood for an electric arc furnace having openings in the roof for the passage of heating electrodes therethrough, comprising a circular enclosure for mounting on the furnace roof about the electrodes and having electrode openings therethrough, means in fluid flow communication with said collector conduit connecting said enclosure to means for exhausting air from the enclosure, and baflie means mounted in said enclosure about a portion only of an electrode opening and being of a size and shape so as to Patented Nov. 10, 1970 provide a substantially equal pressure drop across the entire area of electrode opening when suction is applied to the enclosure.

BRIEF DESCRIPTION OF THE DRAWINGS Reference is made to the accompanying drawings, in which:

FIG. 1 is a perspective view of a furnace hood of the present invention with the electrodes shown in dotted lines;

FIG. 2 is a sectional view taken along lines 22 of FIG. 1;

FIG. 3 is an elevational sectional view of an alternate embodiment of the invention; and

FIG. 4 is a perspective view partially broken away, of the adjustable bafiie for alternate embodiment as shown in FIG. 3.

DETAILED DESCRIPTION In accordance with the instant invention, a hood is provided which insures complete fume control with minimum amounts of air flow. This is accomplished by providing a circular enclosure about the electrodes with openings and baflle means arranged so as to provide a substantially equal pressure drop across the entire area of electrode opening when suction is applied and a flow of ventilation air downward along the electrodes and into a concentric collector duct.

Referring to the drawings, FIGS. 1 and 2 show a furnace hood 10 comprising a circular enclosure 11 in fluid flow communication with a conduit 12. The conduit 12 has a discharge end 13 in alignment with the intake end of a conventional dust collector and suction source (not shown). The suction source can suitably be a fan. The circular enclosure comprises a top wall 14, a bottom wall 15, and one side wall 16. The top wall 14 is provided with an opening 17 which is concentric with the electrode 18 protruding through the roof of the furnace. In like manner, the bottom Wall has a circular opening 19, also concentric about the electrodes 18. Depending from the top wall 14 is a baffle 20 which extends about a portion only of opening 17. The baffle 20 is a partially annular ring of a height less than that of the side wall 16 of the enclosure 11.

The top wall 14, bottom wall 15, side wall 16 and baflle 20 define a concentric collector duct 21 which is concentric about the electrodes 18. The side wall 16 is provided with dilution air ports 22 having gates 23 for adjusting the flow of air into the collector duct 21.

Hood 10 is supported from above by any suitable means such as from the roof ring or roof support beams. A slight clearance A exists between the bottom wall 15 and the upper furnace roof surface to allow for dilution air to constantly sweep and cool the roof as well as to prevent damage to either the roof or hood by reason of the roof heaving.

An alternate embodiment of the invention is illustrated in FIGS. 3 and 4. As in the hood illustrated in FIGS. 1 and 2, there is provided a circular enclosure 31 about the electrodes 38. The circular enclosure comprises a top wall 34 having an opening 37 concentric about the electrodes 38, a bottom wall 35 also provided with an electrode encircling opening 39, and a side wall 36 with dilution air ports 42 spaced thereabout. Adjustably mounted to the top wall 34 is a baffle 40. The top wall 34, bottom wall 35, side wall 36 and baflle 40 define a collector duct 41 which is concentric about the electrodes 38.

The baffle 40 is provided with a sleeve 43, coextensive with the baflle ring 44, which rides in tracks 45 and can be raised or lowered by means of adjustable arms 46 extending through the top wall 34 to vary the height of the baffle. The adjustable arms 46 are each provided with a handle 47, locking pin 48, and pin holes 49 to enable the sleeve 43 to be moved and locked into position. The amount of fumes given off by a furnace can vary and the air flow for greatest economy is proportioned to match fume generation. Thus, the sleeve 43 can be raised or lowered as conditions change to insure that in all cases a substantially equal pressure drop will exist across the entire area of electrode openings in the enclosure 31.

The hood illustrated in FIG. 3 also has a sealing ring 50 coextensive with the side wall 36 and movably attached thereto by means of chains 51. This feature has the advantage that if the heat of the furance should cause the furnace roof to become distorted during operation the sealing ring, which may be of flexible construction, will remain in intimate contact with the roof at all points. Thus the pressure drop across the electrodes will not be adversely affected by undesirable dilution air being drawn into the collection duct 21 by virtue of the gap created between the furance roof and the lowermost side wall portion of the hood. It is also possible that during some applications, the hood itself if not provided with the sealing ring could also become warped by virtue of the sidewall being in direct contact with the room. This also would cause improper air distribution and difliculty in maintaining an equal pressure drop across the electrode opening. By means of the seal ring 50, the bottom wall of the enclosure can be kept off the roof surface 52, and, moreover, an opening 53 provided about the entire periphery of the enclosure 31 to permit dilution air to sweep over the surface of the roof to collect fumes trying to escape thereover and also to cool the surface of the roof. The movement of the ventilation air through opening '37 and dilution air through the openings 53 and ports 42 is depicted by arrows.

The operation of the hood of the present invention is evident from the description set forth above, and will be further described in connection with the embodiment shown in FIGS. 1 and 2. The enclosure 31 is placed on the roof of an electric arc furnace about the electrodes 18. When suction is applied, ventilation air passes downwardly over the electrodes 18 acting to cool them and to sweep the fumes and dust rising counter-current thereto from the furnace into the concentric collector duct 21. Dilution air, in varying amounts, can be added to the collector duct 21 through the ports 22 to provide external final adjustment if desired. The baflle 20 insures that a substantially equal pressure drop across the openings 17 and 19 will result to prevent escape of fumes and dust due to a low pressure at the area of the collector duct 21 most remote from the suction source.

As to materials, the elements of the hood are preferably made of metals which are resistant to high heat. With respect to the electrode openings, they must be of a size suflicient to permit ready passage of the electrode therethrough into the furnace without any interference. Thus, a separate hole could be provided for each electrode used in the furnace, or a single opening as set forth in FIG. 1. It is preferred, however, not to have too large a gap between the side of the electrode and the top opening in the conduit, since as the size of the gap increases the larger volume of air flow must be utilized to prevent escape of the gases from the conduit. In like manner, the height and shape of the distribution baflle is preferably C-shaped, as shown in FIG. 1, although other shapes can be used, dependent upon the particulars of the electrode opening, so long as a substantially equal pressure drop across the entire area of electrode opening is obtained.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purposes of illustration which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A hood for electric arc furnaces having openings in their roofs for passage of heating electrodes therethrough into the furnace, comprising a circular enclosure adapted to be mounted on the furnace roof, said enclosure having a top wall, a bottom wall, a side wall, an electrode opening in each of the top wall and bottom wall, and baflle means depending from the top pwall and extending about a portion of the electrode opening in the top wall, said walls and bafile means defining a duct concentric about the electrodes for collecting fumes and dust emitted by the furnace and said baffle means being of a size and shape so as to provide a substantially equal pressure drop across the entire area of electrode openings when suction is applied, and means in fluid flow communication with said concentric collector duct for connecting said duct to a suction source.

2. The hood of claim 1 in which the side wall is provided with at least one port for the admission of dilution air into the concentric collector duct.

3. The hood of claim 1 wherein the baflle means is a partially annular ring of a height less than that of the side wall of the enclosure.

4. The hood of claim 1 including a sealing ring about the exterior of the side wall and movably attached thereto.

5. The hood of claim 3 wherein the baffle means includes an adjustable sleeve in engagement with the annular ring and substantially coextensive therewith and means attached to the sleeve for moving the sleeve relative to the annular ring thereby varying the height of the battle.

6. The hood of claim 2 wherein said port is provided with means for adjusting the amount of air flowing therethrough into the concentric collector duct.

7. A hood for electric arc furnaces having openings in their roofs for passage of heating electrodes therethrough into the furnace, comprising a circular enclosure adapted to be mounted on the furnace roof, said enclosure having a top wall, a bottom wall, a side wall, a trefoilshaped electrode opening in the top wall, a circular electrode opening in the bottom wall, and a partially annular ring of a height less than that of the side wall depending from the top wall about a portion of the trefoil-shaped electrode opening, said walls and annular ring defining a duct concentric about the electrodes for collecting fumes and dust emitted by the furnace, and a conduit in fluidflow communication with said concentric collector duct for connecting said duct to a suction source.

8. The hood of claim 7 including ports communicating with said concentric collector duct spaced about the side wall of the enclosure, said ports having means for adjusting the amount of air flowing therethrough into said duct.

9. A hood for electric arc furnaces having openings in their roofs for passage of heating electrodes therethrough into the furnace, comprising a circular enclosure, said enclosure having a top wall, a bottom wall, and a side wall, an electrode opening in each of the top wall and bottom wall, and an adjustable batfle means depending from the top wall about a portion of the opening in the top wall, said walls and baffle defining a duct concentric about the electrodes for collecting fumes and dust emitted by the furnace, a conduit in fluidflow communication with said concentric collector duct for connecting said duct to a suction source, and a sealing ring about the exterior of the side wall and movably attached thereto and adapted to rest on the furnace roof, said adjustable baflie means including 'a partially annular ring, a sleeve in engagement With the annular ring and substantially coextensive therewith, and means attached to the sleeve for moving the sleeve relative to the annular ring thereby varying the height of the baffle.

10. The hood of claim 9 including ports communicating with said concentric collector duct spaced about the side wall of the enclosure, said ports having means for adjusting the amount of air flowing therethrough into said duct.

11. A hood for an electric arc furnace having an opening in the roof thereof for passage of heating electrodes therethrough into the furnace, comprising enclosure means adapted to be mounted on the furnace roof, said enclosure means having top wall means bottom wall means, side wall means, an electrode opening in each of the top wall means and bottom Wall means, said wall means defining a duct substantially concentric about the electrodes for collecting fumes and duct emitted by the furnace, bafile means within said duct for providing a substantially equal pressure drop across the entire area of electrode openings when suction is applied, and means in fluid flow communication with said collector duct for connecting said duct to a suction source.

References Cited UNITED STATES PATENTS 4/1960 Pierce 13-9 5/1960 Ortaies.

US. Cl. X.R. 

